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Old 04-16-2013, 05:48 PM   #1
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Adding lead acid batteries to a bank for more capacity


Is there a proper method to adding more batteries to a battery bank in order to get more capacity? For example do they need to be at the same charge rate, or will they automaticly equalize during charging?

Also if the existing batteries are close to a year old, will there be any issues? I do plan to get the proper equipment so I can safely add a bit of distilled water to them so I can top them up if required. What is the proper way to know when this needs to be done? I imagine it will be kind of hard to tell the height of the acid when looking straight down in the hole. Also is this something I can do "live" while they are attached to the circuit? (inverter-charger)

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Old 04-16-2013, 05:52 PM   #2
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Adding lead acid batteries to a bank for more capacity


hydrometer...check the specsific gravity.temp is nedded also to get a good reading....a thermomiter for batteries will show a correction factor for above and below 77*Ffor example,batt reads 1.300 spec gravity,at 80*F add 2 points to hydrometer reading.batteries should be as close as possible in specifications.gharge fate cappicty ect.


Last edited by oleguy74; 04-16-2013 at 05:59 PM.
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Old 04-16-2013, 05:54 PM   #3
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Adding lead acid batteries to a bank for more capacity


I was reading that too but got confused, is that just to check the charge? Isin't it basically like a volt meter but doing it at the chemical level? Or will it still tell me something when it's fully charged? Also not sure where I'd actually buy one of those.
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Old 04-16-2013, 06:35 PM   #4
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Adding lead acid batteries to a bank for more capacity


not so much.specfic gravity will tell you more about the real condition of the batt.1.200 specfic gravity is (or a little more)is a normal full charge.some batteries will read a little higher.also that is the condition of the electrolite(acid)quality.
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Old 04-16-2013, 07:18 PM   #5
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Adding lead acid batteries to a bank for more capacity


Water just has to be above the plates.
Not hard at all to look down and see what the level is.
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Old 04-16-2013, 07:45 PM   #6
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Adding lead acid batteries to a bank for more capacity


As long as the batteries are the same type, you can add more without a problem. Obviously don't mix gel/AGM/flooded cells since they have different optimum voltages. The charge state doesn't really matter, since they will quickly equalize. Installing the new ones while all batteries are fully charged avoids high currents between batteries and won't load down your charging source. That usually isn't a big deal though.
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Old 04-16-2013, 07:51 PM   #7
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Adding lead acid batteries to a bank for more capacity


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Originally Posted by mpoulton View Post
As long as the batteries are the same type, you can add more without a problem. Obviously don't mix gel/AGM/flooded cells since they have different optimum voltages. The charge state doesn't really matter, since they will quickly equalize. Installing the new ones while all batteries are fully charged avoids high currents between batteries and won't load down your charging source. That usually isn't a big deal though.
Accurate Key point there.....lead acid/gell cells/AGM, etc. are voltage limited when it comes to charging....They do not self limit on voltage like NiCads do. So if your charger limits the voltage to the correct level for the batteries....your ok....each battery will pull as much current as it needs until charge.

Obviously, the charger also has a current limit.....
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Old 04-16-2013, 09:11 PM   #8
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Adding lead acid batteries to a bank for more capacity


Good to hear, I'll actually be buying the same model of battery, so I should be good. So when one talks about "charge" when checking electrolyte, is this different then "charge" as far as voltage goes? I think that may be where I'm getting confused. As for water level, is that all that matters, that it's above the plates? I figured it was more specific than that. Is there a point where I may need to add acid? ex: if gravity is too low? (or high?) or is it always water? I'm guessing the hydrogen they produce comes only from the water, and not the acid? I want to make these last as long as possible, even if it requires a bit more work. I'm thinking I can probably do a routine maintenance on them every 6 months or something.

I saw on the Canadian Tire website they do sell hydrometers, so when I go pickup my two extra batteries I'll pick one up along with some safety gloves, face mask/glasses and a funnel. Of course, I'll have to grab distilled water at the grocery store too.
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Old 04-17-2013, 02:01 PM   #9
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Adding lead acid batteries to a bank for more capacity


What size batteries are you dealing with ?
The bigger they are, the more important it is to have the new and old batteries at about the same charge level before adding batteries to the bank. Otherwise you can set up tremendous currents between the batteries.

Adding new batteries to an old bank is not a good idea if there is a significant age difference. the old batteries can hamper the performance of the new batteries. Since yours are less than a year old, it is not a problem in your case.

Checking the battery "charge level" or specific gravity with the hygrometer gives you an idea of how each cell is performing. With a volt meter, you get an total reading. If the reading is 12.62 volts you don't know whether the battery is 90% charged, or you could have 5 charged cells, with one cell at a lower state of charge.

Here are the Trojan Battery instructions on watering batteries.
If you click the links in the box on the lower right, you can learn a lot about the "care and feeding" of batteries.
http://www.trojanbattery.com/Battery.../Watering.aspx

Inspecting the batteries for water level and performing any required maintenance should be a once a month, not every 6.
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Old 04-17-2013, 06:02 PM   #10
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Adding lead acid batteries to a bank for more capacity


Let's be clear here: batteries can be fully destroyed in weeks, not years, if drawn down too far and left that way. One year old should be fine IF they've been treated properly. Sounds like you know what you're doing - just want to make that clear to readers.

Also, for anyone reading this, there's little justification in buying regular Pb acid batteries these days for PV systems. Buy the sealed ones and you have zero maintenance at little extra cost. You do need a first-class charge controller because even a little over-charging shortens their life greatly.
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Old 04-17-2013, 06:17 PM   #11
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Adding lead acid batteries to a bank for more capacity


The batteries I am dealing with are 12v marine batteries, they're 100AH, 12v. I bought two more, I'll be maintaining the existing two before I add the two new ones to the bank. The reason I went with these over sealed is the cost. Sealed are about 2 to 3 times the price.

My setup is standby, so the batteries are on a trickle charger (smart, so it should stop/go as required) and if the power goes out it immediately switches to inverter. It's a Tripp Lite inverter-charger. So only time the batteries actually work is when the power goes out. They've been run down about 2 to 3 times so far, and by run down I mean the inverter charger stopped. So I imagine/hope it's designed to stop at a state that is safe for the batteries. Voltage went down to about 10.4 while under load. It was 11ish with no load after it shut down. They are never left in an uncharged state, unless there would be an extended power outage then they'll be run down till the power comes back, but we're talking hours and not days. Hopefully with the two more they'll also be working less hard now when the power does go out.

Read that trojan site and other sites on hydrometers, think I'm good now! So essentially I need to test when the batteries are fully charged (in my case pretty much any time as they should be in float mode) and the value should be around 1.265 at normal operating temperature of 26C. Mine are probably running slightly lower so I guess a slightly lower gravity should be ok. Given I have two brand new batteries think I'll charge them up and then test and use those as reference.

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Old 04-17-2013, 07:59 PM   #12
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Adding lead acid batteries to a bank for more capacity


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The batteries I am dealing with are 12v marine batteries, they're 100AH, 12v. I bought two more, I'll be maintaining the existing two before I add the two new ones to the bank. The reason I went with these over sealed is the cost. Sealed are about 2 to 3 times the price.

My setup is standby, so the batteries are on a trickle charger (smart, so it should stop/go as required) and if the power goes out it immediately switches to inverter. It's a Tripp Lite inverter-charger. So only time the batteries actually work is when the power goes out. They've been run down about 2 to 3 times so far, and by run down I mean the inverter charger stopped. So I imagine/hope it's designed to stop at a state that is safe for the batteries. Voltage went down to about 10.4 while under load. It was 11ish with no load after it shut down. They are never left in an uncharged state, unless there would be an extended power outage then they'll be run down till the power comes back, but we're talking hours and not days. Hopefully with the two more they'll also be working less hard now when the power does go out.
Yup, sealed are typically 300-400 AH but you do get what you pay for. I expect you know that marine so-called "deep cycle" are not recommended for PV, and it sounds to me like you've been driving the marine's pretty hard so adding more might just not work. Be very careful to have the old ones fully charged before you hook up the new ones.
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Old 04-17-2013, 08:54 PM   #13
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Adding lead acid batteries to a bank for more capacity


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Yup, sealed are typically 300-400 AH but you do get what you pay for. I expect you know that marine so-called "deep cycle" are not recommended for PV, and it sounds to me like you've been driving the marine's pretty hard so adding more might just not work. Be very careful to have the old ones fully charged before you hook up the new ones.
Actually they're not for PV, but for standby power backup, but good to know they're not recommended for PV as I have been pondering on setting such a system up too and would have just hooked it up to those batteries or other similar ones. These are the best bang for the buck. This current setup is for standby power so they are always on a float charge.

Did not know sealed were higher AH though... I assumed they were all 100 as well. Guess it's definitely something to consider in the future if I expand or build a new system. I eventually want to also backup my TV and computer, and possibly furnace, so I could always use this system for that and build a even higher capacity system for the servers in the future.

Not sure if I've driven them too hard yet other than a few discharges, hard to tell if the run time is good or not as I did add a bit more equipment and never measured it again so perhaps the 3ish hours I got off them is still good. I need to find a permanent way to measure watt/amps so I can just always know how much I'm drawing even if I plug something new.
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Old 04-17-2013, 09:13 PM   #14
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Adding lead acid batteries to a bank for more capacity


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I need to find a permanent way to measure watt/amps so I can just always know how much I'm drawing even if I plug something new.
It's called a shunt and is usually installed right next to the inverter. It's just a chunk of metal with a very precise and low resistance, wired in series in one of your battery cables, usually the hot because 12 V is not generally dangerous It of course still needs to be in a electrical box of some kind. You then need to measure voltage drop across the shunt which translates directly into amps. Go to any PV store and they should be able to set you up with what you need. The cadillac meter versions (with some not-all-that-simple programming) will tell you % charge in your battery string.
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Old 04-17-2013, 09:21 PM   #15
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Adding lead acid batteries to a bank for more capacity


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It's called a shunt and is usually installed right next to the inverter. It's just a chunk of metal with a very precise and low resistance, wired in series in one of your battery cables, usually the hot because 12 V is not generally dangerous It of course still needs to be in a electrical box of some kind. You then need to measure voltage drop across the shunt which translates directly into amps. Go to any PV store and they should be able to set you up with what you need. The cadillac meter versions (with some not-all-that-simple programming) will tell you % charge in your battery string.
Good to know. So basically something like these?

http://www.ebay.ca/itm/DC-4-5-30V-10...item3cd0182b21

or this:
http://www.ebay.ca/itm/Analog-Amp-Pa...item19c857fe38

I could install them on a blank panel that would go into my server rack. Would look pretty sharp.

Edit: Actually to keep things simple think I could just do the AC output side, and use these:

http://www.ebay.ca/itm/High-Quality-...item257bf20a87

Would that be fine? I'd want the back to be in some kind of electrical box of course, and possibly fused (as oppose to relying on the 15 amp breaker or any fuse in the UPS).


Last edited by Red Squirrel; 04-17-2013 at 09:26 PM.
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